One Nation deal squared if I lose: McGowan

If he loses Saturday's state election, Western Australian Labor leader Mark McGowan predicts a Liberal-One Nation preference deal will be replicated nation-wide.

The opposition leader hit out at the arrangement, which he says is all about maximising the Liberal vote two days out from polling day.

"If we lose, One Nation will be at the centre of political activity, certainly in regards to the Liberal Party, across Australia," he told ABC radio on Thursday.

Mr McGowan said he would deal with One Nation representatives in the upper house by presenting good legislation and arguing the case for its passage.

He insisted Labor was still the underdog because it needed to win 10 seats to form government.

"The Liberal Party is doing everything it can to try and hold onto office, including its deal with One Nation," he said.

Repaying the state's debt would take decades, but Mr McGowan predicts a return to surplus in the next couple of years.